The invention concerns a multilayer body having microlenses and a process for the production thereof.
Multilayer bodies having microlenses and identical repetitive microimages arranged under the microlenses are used as security elements for security documents such as for example bank notes and ID cards.
Thus for example U.S. Pat. No. 5,712,731 discloses such an arrangement of a microlens grid raster and a microimage grid raster formed by a plurality of identical microimages arranged in accordance with the microimage raster. The microlenses arranged in a microlens array produce a copy of the microimages, that is enlarged in pixel fashion, so that an enlarged representation of the microimage becomes visible to the viewer. As the pixel, which is respectively represented by the microimages, of the respective microimage changes in dependence on the vertical and horizontal viewing angles, such an arrangement of a microlens raster and a microimage raster with identical microimages exhibits an optically variable effect, that is to say the microimage which is enlarged for the viewer appears to move when the arrangement is turned and/or tilted. The image produced can be in front of or behind the plane of the substrate.
In the production of such arrangements it is necessary for microimages to be formed with a very high resolution in a layer of the multilayer body. In that respect the production of microimages with gray value or color gradations has proven to be particularly problematical so that this image-generation process is at the present time restricted to simple, monochrome motifs and themes such as alphanumeric characters and simplistic logos.